Posted on 05/28/2016 11:29:45 PM PDT by 2ndDivisionVet
Researchers at MIT are seeking to redesign concrete — the most widely used human-made material in the world — by following nature’s blueprints.
In a paper published online in the journal Construction and Building Materials, the team contrasts cement paste — concrete’s binding ingredient — with the structure and properties of natural materials such as bones, shells, and deep-sea sponges. As the researchers observed, these biological materials are exceptionally strong and durable, thanks in part to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible, level.
From their observations, the team, led by Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (CEE), proposed a new bioinspired, “bottom-up” approach for designing cement paste.
“These materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” Buyukozturk says. “We want to see what kinds of micromechanisms exist within them that provide such superior properties, and how we can adopt a similar building-block-based approach for concrete.”
Ultimately, the team hopes to identify materials in nature that may be used as sustainable and longer-lasting alternatives to Portland cement, which requires a huge amount of energy to manufacture.
“If we can replace cement, partially or totally, with some other materials that may be readily and amply available in nature, we can meet our objectives for sustainability,” Buyukozturk says.
Co-authors on the paper include lead author and graduate student Steven Palkovic, graduate student Dieter Brommer, research scientist Kunal Kupwade-Patil, CEE assistant professor Admir Masic, and CEE department head Markus Buehler, the McAfee Professor of Engineering.
“The merger of theory, computation, new synthesis, and characterization methods have enabled a paradigm shift that will likely change the way we produce this ubiquitous material, forever,” Buehler says. “It could lead to more durable roads, bridges, structures, reduce the carbon and energy footprint, and even enable us to sequester carbon dioxide as the material is made. Implementing nanotechnology in concrete is one powerful example [of how] to scale up the power of nanoscience to solve grand engineering challenges.”
From molecules to bridges
Today’s concrete is a random assemblage of crushed rocks and stones, bound together by a cement paste. Concrete’s strength and durability depends partly on its internal structure and configuration of pores. For example, the more porous the material, the more vulnerable it is to cracking. However, there are no techniques available to precisely control concrete’s internal structure and overall properties.
“It’s mostly guesswork,” Buyukozturk says. “We want to change the culture and start controlling the material at the mesoscale.”
As Buyukozturk describes it, the “mesoscale” represents the connection between microscale structures and macroscale properties. For instance, how does cement’s microscopic arrangement affect the overall strength and durability of a tall building or a long bridge? Understanding this connection would help engineers identify features at various length scales that would improve concrete’s overall performance.
“We’re dealing with molecules on the one hand, and building a structure that’s on the order of kilometers in length on the other,” Buyukozturk says. “How do we connect the information we develop at the very small scale, to the information at the large scale? This is the riddle.”
Building from the bottom, up
To start to understand this connection, he and his colleagues looked to biological materials such as bone, deep sea sponges, and nacre (an inner shell layer of mollusks), which have all been studied extensively for their mechanical and microscopic properties. They looked through the scientific literature for information on each biomaterial, and compared their structures and behavior, at the nano-, micro-, and macroscales, with that of cement paste.
They looked for connections between a material’s structure and its mechanical properties. For instance, the researchers found that a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks. Nacre has a “brick-and-mortar” arrangement of minerals that generates a strong bond between the mineral layers, making the material extremely tough.
“In this context, there is a wide range of multiscale characterization and computational modeling techniques that are well established for studying the complexities of biological and biomimetic materials, which can be easily translated into the cement community,” says Masic.
Applying the information they learned from investigating biological materials, as well as knowledge they gathered on existing cement paste design tools, the team developed a general, bioinspired framework, or methodology, for engineers to design cement, “from the bottom up.”
The framework is essentially a set of guidelines that engineers can follow, in order to determine how certain additives or ingredients of interest will impact cement’s overall strength and durability. For instance, in a related line of research, Buyukozturk is looking into volcanic ash as a cement additive or substitute. To see whether volcanic ash would improve cement paste’s properties, engineers, following the group’s framework, would first use existing experimental techniques, such as nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction to characterize volcanic ash’s solid and pore configurations over time.
Researchers could then plug these measurements into models that simulate concrete’s long-term evolution, to identify mesoscale relationships between, say, the properties of volcanic ash and the material’s contribution to the strength and durability of an ash-containing concrete bridge. These simulations can then be validated with conventional compression and nanoindentation experiments, to test actual samples of volcanic ash-based concrete.
Ultimately, the researchers hope the framework will help engineers identify ingredients that are structured and evolve in a way, similar to biomaterials, that may improve concrete’s performance and longevity.
“Hopefully this will lead us to some sort of recipe for more sustainable concrete,” Buyukozturk says. “Typically, buildings and bridges are given a certain design life. Can we extend that design life maybe twice or three times? That’s what we aim for. Our framework puts it all on paper, in a very concrete way, for engineers to use.”
This research was supported in part by the Kuwait Foundation for the Advancement of Sciences through the Kuwait-MIT Center for Natural Resources and the Environment, the National Institute of Standards and Technology, and Argonne National Laboratory.
You have nailed it twice and for me the word “sustainable” and the sentence below was all I needed to know. BEE ESS!!!
These guys are just hunting for Grant money, their ideas are impractical.
Slogging through through the buzz words, I came to the same conclusion,
I don't see this as BS.
I worked a few biomedical research studies as project statistician (of course), and they put in an AIDS reference whenever they could. If you deleted those references, which were true in the sense that the work applied to many conditions including some associated with AIDS, what you had left were excellent research proposals. I think the sustainability nonsense is there for the same reason, purely to make scientifically-illiterate liberals happy. What they are really looking at is the structure of concrete as an organized rather than randomly mixed composite material - whether it can be made stronger either along specified axes or overall by controlling that structure. "Sustainability" is just a buzz word that adds to their odds of funding without detracting from the quality of the science.
“with the structure and properties of natural materials such as bones”
Made by Yoyodyne?
Wow! “Buyukozturk” is my middle name!
Excellent point...PC buzzwords to give real science a chance!
Do you assess this research as valid, or just having the potential to be valid?
Even so, I’m not sure that is the goal. I think they are referring to them by analogy. Seashells are much stronger and more durable than the same materials are used by humans to build. It is the microstructures and controls that need to be learned. If we can figure out ways to improve control and create these ultra strong microstructures within the materials, the product can be much stronger, durable, and lighter.
lastly, the term “a random assemblage” is used by the authors when in truth Portland cement concrete for engineering structures is a carefully engineered
It is a ‘random assemblage’ in the sense that it is not a consistent crystalline, lattice, or even colloid form - or assemblage of such. On the micro scale it varies in constituency and molecular arrangement from point to point.
Exactly.
Remember when cinder blocks were promoted as a great advance because of their lighter weight and superior strength?
Concrete mix is like the male member, the stiffer it is the better it works.
I am not a materials scientist, but I see the potential for a lot of value in the ideas behind parts of approach. To a large extent, the paper seems theoretical "let's start thinking about concrete again" rather than a report of results. It also has multiple points.
In terms of materials, concrete has several recipes, depending on the intended application, and the nod in the direction of more variation and tracking the properties of those variations seems like a good idea that could eventually provide a small to moderate benefit.
In terms of mesoscale structure, I expect a much bigger payoff, potentially. Current concrete is a precise and nearly uniform mixture on that scale. The real challenge will be to build with a controlled mesoscale structure (different from rebar, but for similar purposes) at an affordable price. I'm not sure how easy that will be compared with pouring a truckload of concrete and counting on the standard strength of the isotropic mixture. I'm not sure how far we will get in treating concrete like our more sophisticated composite materials, not when the whole point of concrete as it is used today is that it is low-cost and durable. We might find that there is a way of building in that anisotropic structure at an affordable price, and it may even be worthwhile to get high strength concrete at a much lower weight.
All of the above is a wordy way of saying: "Valid? No. Potential? Maybe."
I always thought different levels of stiffness were best for different purposes. Some concrete needs to be as hard as possible. Other times, for example in earthquake zones, a little flex is good.
Re bar handles the flex part. Stiff is always the best.
I now await the screams of horror.
Then why so many types of concrete? I was under the impression that we gave up both strength and stiffness to save weight with the lightweight concretes. I thought you would get better thermal and shock durability but less stiffness with extra air in either the aggregate or the mortar for the lightweight mixes. The same for polymer concretes. I assumed that polymers would change (probably reduce) the stiffness. Why add it if stiff is always best, and why only sometimes?
I'm not disagreeing - this is well outside my area. I'm just confused because I've been on the edge of projects where engineers argued over the selection of particular concrete mixes.
The water molecules do not evaporate like drying paint. Concrete cures and does not dry. The water molecules form bonds with the cement. The more water molecules the weaker the concrete.
SUSTAINABLE
The Agenda 21 code word
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